Method and apparatus for sonic dental drilling



y 19, 1964 E. A. VON SEGGERN 3,133,351

METHOD AND APPARATUS FOR some DENTAL DRILLING Filed Feb. 11, 1957 3 Sheets-Sheet 1 INVEN TOR. z flew-"57,4. (/04 556654 May 19, 1964 E. A. VON SEGGERN 3,133,351-

METHOD AND APPARATUS FOR SONIC DENTAL DRILLING Filed Feb. 11, 1957 3 Sheets-Sheet 2 INVENTOR. [EA/E5 r ,4. Vo/v 55a GER/V y 19, 1964 E. A VON SEGGERN 3,133,351

METHOD AND APPARATUS FOR some DENTAL DRILLING Filed Feb. 11, 1957 3 Sheets-Sheet 3 6 av Z97 INVENTOR. 1. mvssr A V0 5GGRVV United States Patent 3,133,351 METHGD AND APPARATUS FQR Sillili? DENTAL DRILLKNG Ernest A. von Seggern', Burbank, Calif, assignor to fioundrive Engine (Iompany, Les Angelles, (Ialiil, a corporation of @alifornia Filed Feb. ll, 1957, Ser. No. 639,34

l4 Elaims. (ill. 32--26) r This invention relates to a sonic method and apparatus for cutting materials, and, because it finds great utility in its application to dentistry by literally polishing a hole into a tooth, or in other words to a form of dental drilling, embodiments of my invention adapted for such application will be described hereinafter, it being understood that the invention is not limited to such application.

The general subject of cutting by use of sonically actuated abrasive particles is covered in Reissue Patent No. Re. 23,657 of May 19, 1953. As disclosed in said patent, it is desirable to have a component of motion of the tool perpendicular to the surface of the progressive cut, even when unbalanced or angled tools are used. In this connection said patent discloses that if desired to vary the pattern of the paths of contact of the surface finishing elements with the surface being treated, the surface may be disposed at any desired angle with the direction of propagation of the sound waves adjacent thereto. This invention is concerned with my discovery of the importance of a particular characteristic pattern for such component motion, and with my further invention of a method and apparatus for accomplishing this characteristic motion.

It is an object of this invention to employ sonic wave principles to cause cutting, including the removal of small projections and indentations, without scu'ffing action, peening, or local surface heating. The term sonic Wave or sound wave as employed herein includes condensation or compression and rarefaction or tension impulses of frequencies not only with the auditory range, but also other and higher frequencies, which impulses travel with the speed of sound waves through an elastic medium. lvloreover, my invention contemplates lateral elastic vibrations of these frequency ranges in particular combinations with such longitudinal vibrations.

The frequency of the sound waves generated and the distance between the sound wave generation locus and the locus of sound wave reflection utilization may be so related that the reflected impulse reaches the generating locus and is reflected therefrom. at such time as to reinforce or amplify each newly generated impulse. The newly generated impulse reinforced by the first reflected impulse may be again reflected from the interface, this second reflected reinforced impulse again returning to the generating source to reinforce in its turn a newly generated impulse. Each such reinforcement by reflection adds to the value of each newly generated impulse, so that impulses traveling through the elastic medium reach a value considerably greater than and under suitable conditions many times the value of the generated impulse. When the factors specified have been properly related to secure this reflection and reinforcement'of the generated sound wave, a condition of resonance is established within the elastic medium.

Each compression impulse transmitted through the elastic medium is followed by a rarefaction or tension impulse. When a condition of resonance is established Within the medium, there is a zone of maximum pressure variation which may be adjacent the impulse generator, and at a distance of one wavelength therefrom there is a similar zone of maximum pressure variation.

Halfway between these loci there is a zone also of maximum pressure variation. Under such condition of resonance there occurs therefore, at zones spaced whole numbers of half wavelengths distant from the sound Wave generator, maximum pressure variations. Half Way between adjacent zones of maximum pressure variations occur the zones of maximum velocity variation. in these latter zones located at distances equal toodd multiples of quarter wavelengths, the molecules of the elastic medium are moving with the maximum velocity, alternating their direction of travel so that'they travel in one direction for half of the period of the frequency of the generated impulse and in the opposite direction for the other half with an amplitude which is the summation of the generated and reflected impulses at such zones.

It is contemplated by my invention that the velocity and the amplitude of movement of the molecules of the elastic medium at these zones of maximum velocity variation in the standing or stationary sound wave established under conditions of resonance, or as near these zones as desired, shall be utilized to actuate abrasive particles or elements by their drag thereon into impact with or contact along the surface of an article to be treated.

With respect to M1 forms of the apparatus of my invention herein described, there. may be employed cutting fluid of any desired characteristics, preferably water or oil of suitable viscosity. For the abrasive particles there may be employed full size grains of silicon carbide or aluminum oxide, each of which has several sharp points or edges upon its boundary countour and definite cleavage planes, so that it is individually friable, or sand, or particles of metal, or particles of any material harder than the surface being treated and with sharp edges thereon; The sound wave may be generated not only by generators of the piezo-crystal and magnetostriction bar types, as illustrated and described, but by any other suitable types of generators.

All forms of the apparatus of my invention contemplate that the method of my invention maybe performed therewith to subject the surface being polished to uniform action of the polishing elements throughout the desired area by moving the surface being treated or the sound wave generator to vary'the locus of the surface subjected to the maximum velocities of the contacting elements.

The surface finishing elements at the maximum velocity zones will have the maximum velocity and amplitude of movement. Therefore, the portions of the surface of the article contacting the surface finishing elements at the maximum velocity variation zones are subjected to impact of the particles of the greatest value and during their maximum movement.

it will also be seen that, due to the very great velocity of the surface finishing elements, the surface may be cut or polished at an extremely high rate, while at the same time maintaining a force of impact of the individual surface finishing elements against, and an amplitude of their movement in contact with, the surface being treated of an extremely low order, with the result that there is no objectionable scratching, burnishing, peening, or local surface heating during the polishing of the surface.

Sonic dental drills heretofore proposed comprise a rod capable of transmitting longitudinal elastic compression waves, provided at one end with a drilling tip, and at the other with a sonic vibratory driver, e.g., magnetostriction oscillator. This rod may be progressively reduced in cross section from its driven end towards its drill tip end, either continuously or step tapered, and is sometimes called a born. The magnetostriction oscillator or driver transmits longitudinal compression Waves or pulses along the length of the rod and the drill tip, causing longitudinal vibratory motion thereof. The length of the assembly, including rod, tip and magnetostriction core, is generally made equal to one full wavelength at the frequency of operation of the magnetostriction oscillator such that the device operates at resonance, with a one-wavelength reso nant standing wave extending from end to end. Velocity antinodes of this standing wave occur at opposite ends of the assembly, and the extremity of the drill tip vibrates longitudinally at small amplitude but high velocity. The reduction in cross section toward the drill tip desirably magnifies this amplitude and velocity.

In dental cavity preparation, drill tips extending at an angle to the handle are required for certain work. These have been proposed, in the form of angular tips screwed into the small end of the longitudinally vibratory rod or horn. Such angular tips vibrate with a longitudinal component of motion. However, because of the lateral unbalance provided by the angular tips, uncontrolled lateral components of vibration appear, and the extremities of such angular tips, as heretofore known, are therefore subject to very unpredictable motion paths, giving poor control and feel, and have low drilling rates.

An object of the invention is accordingly the provision of an improved method of sonic angle drilling, and an angle tip sonic dental drill, wherein the tip has a desirable motion path conducive to controlled drilling and maximum penetration rate.

I have discovered in connection with extended laboratory experimentation that the most desirable motion path for the extremity of the drill tip, giving the highest drilling rate, for a given amplitude, and the best feel and control, is an ellipse, with the major axis oriented so as to be along a line substantially normal to the cutting face of the tool or to the work being cut, and with a ratio of major axis to minor axis usually or preferably in the approximate range of three or four to one for tooth material cutting. To secure this highly desirable motion path, I cause the tool to operate not only with a longitudinal wave, but with one or more controlled lateral waves as well. The resonance frequency of one lateral wave is forced off the resonance frequency of the longitudinal wave to a controlled extent. The motion path is the resultant of the several waves. The off-resonance wave component is out-of-phase with the longitudinal wave component, which produces elliptical motion. The invention provides for such a controlled degree of such outof-phase lateral wave motion as produces an elliptical motion oriented and shaped as above stated.

The invention will be best understood from the following detailed description of several illustrative embodiments thereof, reference being had to the accompanying drawings, in which:

FIG. 1 is a view, partially diagrammatic, and partially in elevation and partially in section, showing an embodiment of the invention; FIG. 2 is a view of the drill shank of FIG. 1, looking from the right as seen in FIG. 1; FIG. 3 is a diagram of the motion path attained for the extremity of the drill shank of FIG. 1; FIG. 4 is a detailed elevation taken in accordance with line 44 of FIG. 1; FIGS. 5a, 5b, and 5c are diagrams showing, respectively, longitudinal, first lateral, and second lateral standing wave patterns typical or characteristic of the drill shank of FIGS. 1 to 4; FIG. 6 is a perspective view of a modification of the drill shank of FIGS. 1 to Sc; FIG. 7 is a side elevational view of a modified pin-insert form of drill shank, which may be used with the magnetostriction driver of FIG. 1; FIG. 7a is a transverse section on line 7a7a of FIG. 7; FIG. 8 is an edge elevational view of the drill shank of FIG. 7; FIG. 9 is an enlarged detail, in section, of the lower end portion of the drill shank of FIG. 7, showing the pin-insert drill tip in position; FIGS. 10 and 11 are diagrammatic views of the drill shank of FIG. 7 showing, respectively, typical or characteristic longitudinal and lateral standing wave patterns set up therein; FIG. 12 is a partially diagrammatic view, partially in section, showing another embodiment of magnetostriction driver and drill shank; FIG. 12a is a section taken on line 12a-12a of FIG. 12; FIG. 13 is an elevational view of the drill shank, looking from the right in FIG. 12; and FIG. 14 is an elevational view of the drill shank, looking from the left in FIG. 12.

In FIG. 1 of the drawings, the numeral 10 designates a conventional magnetostriction driver or oscillator, having core 16a with winding 11, numeral 12 designates an elongated, elastic coupling means or adapter connected to one end of core 10a, and numeral 13 an angle drill shank coupled to adapter 12.

Adapter 12, which is composed of an elastic metal, is preferably made of ball-bearing steel, because of low internal damping of that material. This adapter 12 has a flat end 12a which is fastened, as by silver soldering, to the adjacent end of core 10a. Extending into the opposite end of the adapter, and continuing for a major portion of the length thereof, is a tapered bore 14, furnished in its mouth with taper threads 15. The corresponding extremity of the adapter may be furnished with wrench faces 16. As here shown, the'adapter 12 tapers from its end 1211 for a distance beyond the inner end of opening 14, as at 12b, and has a slight divergence toward its other end, as shown. The hollow formed by the tapered bore 14, together with the taper at 12b lightens the adapter in the direction from its driver toward its driving end, and thereby increases the amplitude of longitudinal vibration at the driving end, in a manner well understood in the art. Such a tapered member is usually referred to in the art as a horn.

Shank 13 is a one-piece device comprising a flat parallel faced shank portion 20, tapered longitudinally, as seen in the aspect of FIG. 2, and having an integral angularly bent tip section 21, the bend 22 being in a plane at right angles to the planes of the tapering side faces 20a, and as here shown, being at about 30. At its opposite end, the shank has an enlarged head 23, including a taper threaded coupling pin 24 screwed into adapter 12, and a hexagonal portion 25 affording wrench faces 26. The converging lateral edges 20b of the shank merge smoothly, on slight concave curves, with head portion 25 just below wrench faces 26, while the parallel shank faces 20a are merged with the enlarged head portion 25 on substantially 45 angles as indicated at 27. The taper of the shank in the illustrated embodiment extends for about two-thirds the distance down to the bend in the shank, and the shank then has substantially parallel edges to or just slightly short of the bend 22, at which point it is narrowed, so as to form shoulders 28 beyond which it may extend at reduced width to the end of tip section 21.

The relative dimensions and shaping of the shank 13 are made such that three principal standing waves are set up therein, at predetermined frequencies and predetermined phase relations, and these comprise a longitudinal wave and first and second lateral waves, diagrammed respectively in FIGS. 5a, 5b, and 5c.

The longitudinal wave will first be considered, being the wave directly excited by the magnetostriction driver 10, and from which the energy for the two lateral waves is derived. The magnetostriction driver core 10a, the adapter 12 and the bit 13 form a full wavelength, elastic longitudinally vibratory standing wave system, with nodes at n and n (see FIGS. 1 and 5a), and loops as shown, antinodes occurring at the longitudinal extremities and between nodes n and n. The diagrammed longitudinal standing wave pattern 1 shows that vibration is substantially zero at the node n and progressively increases toward the extremity of the shank. Dimensions and relative distribution of mass are preferably made such that the node 11 occurs within the relatively heavy section within the bit coupling, as diagrammed. From the node n, i.e., from the bit coupling, to the extremity of the bit,

,5; is a quarter wavelength distance of the longitudinal standing wave generated in the system at its driven frequency.

In the illustrated embodiment of FIGS. 1-50, the so- .called first lateral wave, wll, has four nodes along the bit shank, with corresponding loops, as indicated in FIG. b, the first of these being located at the coupling, the last near or at the bend 22. The angular portion of the shank is a quarter wavelength long. The second lateral wave, W2 (FIG. 50), has its last node between the bend and the tip, and the next to last above the bend, as illustrated. It will be understood that, whereas vibratory motion in the longitudinal mode occurs longitudinally of the bit shank, the lateral waves occur in directions laterally or transversely of the bit shank, in planes at right angles to the flat faces 20a. It will further be understood that such lateral waves are excited because of a carefully controlled dynamic lateral unbalance of the bent shank, and receive the driving energy from the longitudinal wave.

The first lateral wave (FIG. 5b) is tuned to a resonent frequency matching that of the longitudinal wave, which, in practice, may be accomplished by starting with a shank which is slightly overthick, and grinding on its sides until a resonant standing wave pattern, with the definite loops and nodes, is attained.

It is of first important that the major axis of motion of the tip of the drill be substantially normal to the cutting face, and the attainment of this condition depends upon the longitudinal wave and the first lateral wave. The desired condition depends upon location of the last node of the first lateral Wave in the bend region of the shank. I may accomplish the fixing of this node in the bend in either of two ways, as here shown, by a relatively abrupt change in cross section, accomplished by use of the aforementioned shoulder formations 28. The other expedient, shown in FIG. 6, involves the use of a shank 13a generally like that of FIGS. l4, but having lumped mass 1311 at the bend, atthe desired location of the node.

It is a major feature of the invention that an elliptical path be provided for the tip, with its major axis at right angles to the cutting face, and that the ratio of major axis to minor axis be a substantial number such as three or four to one. This is accomplished by means of the second lateral wave, and by tuning the same to have a higher resonant frequency than that of the'longitudinal and first lateral waves, such that it will be out-of-phase therewith to a predetermined extent. Elliptical motion is obtained by combining two controlled motions which are properly out-of-phase and moving in different determinable directions. In this case, the first motion is that resulting from the in-phase longitudinal and lateral waves, and the secend is a motion which is due to the second lateral wave, oriented directionally substantially parallel to the end surface of the tip. When these are out-of-phase, an elliptical motion is produced.

An elliptical motion of the character heretofore described can be obtained by tuning the second lateral wave to a resonant frequency a suificient degree, either higher or lower, than the resonant frequency of the longitudinal and first lateral waves. However, if'tuned lower initially, shortening of the tip with wear will raise the second lateral resonant frequency and cause the second lateral wave eventually to pass through a peak resonance condition. When this occurs, all the energy in both lateral waves tends to go into that one lateral node to the exclusion of the other, causing the desired pattern to be lost entirely. When tuned on the high side, however, tool wear simply detunes the second lateral, thus gradually decreasing the fatness of the ellipse. To secure initial tuning on the high side, the resonant frequency of the second lateral is raised a controlled amount above the resonant frequency of the longitudinal wave, which causes the motion path gradually to assume the desired elliptical shape, as shown at e in FIG. 3.

As mentioned hereinabove, the second lateral wave 6 should have a node between the tip and the bend, and another node above the bend, with a loop in the region of the bend. To vary the resonant frequency of the second 7 lateral node, so as to secure the off-resonance tuning and desired elliptical motion pathas described above, two procedures are available. To raise the resonant frequency of the second lateral wave (starting from a condition of. resonance at the resonant frequency of the longitudinal wave), the tip section can be gradually shortened, causing the motion path to pass from an elliptical shape, with major axis parallel to the extremity of the tip, through a circular shape, then to the desired shape (FIG. 3), after which the minor axis progressively diminishes as the wave is further detuned. This has proportionately little effect on the longitudinal wave. To lower the resonant frequency of the second lateral wave, if such should be desired, the shank may be thinned at the bend normal to the plane of bending, so as to reduce stifiness at this point.

By thus locally shaping and modifying the dimensions, mass and flexibility of the shank, a combination of the three waves, longitudinal, first lateral, and second lateral is obtained giving the desired elliptical path whose major axis is normal to the cutting face on the end of the tip. If the ellipse is too thin, i.e., if the ratio of major axis to minor axis is much above 4 to l, the amplitude of the second lateral wave is too low, caused generally by tuning of the second lateral too far ofi? resonance. The resonant frequency of the second lateral can be lowered as noted hereinabove to improve the fatness of the ellipse. If the ellipse is too fat, i.e., approaching a circle, the fault is generally insufiicient amplitude in the first lateral wave. This is cured by detuning the scond lateral wave upward, so that the latter takes less energy from the first lateral. This both decreases the minor axis and increases the major axis, more of the available energy being then all cases located in the region of the bend, a node of,

the second lateral should be located between the tip and the bend, and a loop of the second lateral should be located at the bend.

FIGS. 7-9 show a modification employing a removable and replaceable angle tip or hit in the'end of a holder shank which is adapted to be screw coupled to a magnetostriction driver. The purposes include use of relatively inexpensive expendable tips, ready replaceability of tips of different character, all of which will have the proper elliptical motion for optimum cutting, and greater useful tip wear-length.

A magnetostrictive driver and adapter assembly as shown in FIG. 1 may here be used, and will therefore not be again illustrated in connection with this embodiment. Holder shank 44 has a taper threaded coupling pin or plug 45 adaptedto be screwed into the socket of the adapter,

I e.g., the adapter of FIG. 1, and immediately therebelow a hex-head section 46 with wrench faces as shown at 47;

Below the opposite wrench faces 47 of a hex-head sec tion 46, in the aspect seen in FIG. 7, holder shank 44 continues straight downwardly from said faces 47 at uniform width for approximately half its length, and then both tapers and curves somewhat to one side, merging at its lower end into a cylindrical longitudinally bored tipholder head 49 formed with its longitudinal axis at the angle desired for the drill bit or tip, shown at 50. The center of gravity of head 49 will be observed to be somewhat laterally offset from the central longitudinal axis established by the threaded coupling pin 45. This head 49 has a toe 51 at right angles to its length, and a heel 52, which projects downwardly and outwardly from the adjacent edge of the shank 44, so as to allow clearance for the projecting upper extremity of bit 50.

In the aspect at right angles to that of FIG. 7, i.e., in that shown in FIG. 8, the shank 44 is thinned from coupling head 46 to pin holder head 49 to a thickness of the order of one-half, or slightly less, of its greatest width, being, in the illustrated embodiment, just slightly thinner than the diameter of pin holder head 49 (see FIG. 8).

The side faces 54 defining the thin section of shank 44 join the hex-head 46 along angular faces 55 which cut somewhat into said head, and at the bottom merge smoothly into bit-holder head 49. Also, in the illustrated embodiment, and for a later explained purpose, the side faces 54 are formed with longitudinally running hollows or depressions 56, giving the shank an I-beam section, as shown in FIG. 7a.

The angular drill bit or tip 50 comprises a hardened taper pin, fitted into tapered hole 58 extending axially through head 49, and fitted tightly therein by light tapping. The pin is readily removable, when required, by tapping on its end protruding beyond heel 52. The working end of tip 50 may be shaped as required; as here shown, it is thinned on opposite sides, as at 59.

The shaping and dimensions of the shank 44 are such that two principal waves are set up therein, first, a quarter wavelength longitudinal wave, having a node 11' within the mass formed by threaded coupling element 45 and hex-head 46, and an antinode at pin holder head 49 (FIG. 10), and second, a lateral wave having a node 12,, within the mass formed by threaded coupling element 45 and hex-head 46, and a node H in the upper end region of, or just slightly above, the pin holder head 49 (FIG. 11). From node n to the nose 51 of pin holder head 49 is a quarter wavelength, so that an antinode exists at that point. The shank 44 is, in this embodiment, made of sufficient mass relative to that of the tip 50 that these wave patterns prevail with or without the tip 50 in place in the tool. The shank is so designed as to produce a component of linear motion along the angular axis of the tapered hole 58 with or without the presence of tip 50. The installation of the tip 50, of course, necessarily modifies the pattern to some extent, but its relative mass is so small as to minimize this modification, and for all practical purposes, such modification may be ignored.

In this embodiment, only one lateral wave is utilized, and the required elliptical motion is gained by causing it to be out-of-phase with respect to the driving longitudinal wave. In other words, the lateral wave is tuned to be off resonance at the resonant driving frequency of the longitudinal wave.

As in the first described embodiment, a lateral wave is excited by the driving longitudinal wave because of the lateral unbalance of the shank; and it will be seen that the longitudinal curve of the shank and the position of the pin holder head 49 are such as to contribute a material degree of unbalance, without the presence of the insert pin 50. The problem is then to force the excited lateral wave out-of-phase with the longitudinal wave, and this I accomplish in the first instance by so designing the shank that the nodes 11 and In, are well fixed in position. The node n,, is fixed by the use of a fairly large mass, or cross section, at the upper end of the shank, i.e., in the region of the threaded coupling element 45, hex-head 46, and the distribution of mass of the somewhat tapered adapter (adapter 12 of FIG. 1). The lower end node 11 is fixed by reason of the fact that there must be a quarter wavelength distance between it and the free end. It is important to understand that if these nodes can move, to bring the lateral wave into resonance with the driving wave, they will automatically do so; and the fixing of the upper end node, as described above, controls this tendency. Having thus effectively fixed the positions of nodes n and u and assuming for purpose of this discussion that the shank is initially a little overthick as compared with its final thickness dimension, the resonant frequency for the given fixed distance between nodes n and ri is raised above the resonant frequency of the longitudinal wave to the necessary value by thinning the shank laterally, preferably, when using an I-beam section, by thinning the web thereof. This operation removes mass from the shank proportionately more than it reduces lateral stifiness, which has the effect of raising the lateral resonant frequency. This lateral thinning has only slight proportional effect on the longitudinal resonant frequency. Hence, by this process, the shank is brought to such dimensions that the lateral wave has a higher resonant frequency than that of the longitudinal wave, the two will therefore be out-of-phase, and an elliptical motion is obtained. The fatness of the ellipse depends upon the degree of detuning of the lateral wave. In other words, the higher the resonant frequency of the lateral wave above that of the longitudinal wave, the lesser will be the ratio of the major to minor axis of the ellipse. As in the first described embodiment, the optimum ratio is approximately three or four to one.

The orientation of the major axis of the ellipse described by the pin holder head with respect to the axis of the hole 58 requires some attention. I have found that this may be controlled by selectively grinding on the longitudinal edges of shank 44. If the major axis of the ellipse lies originally at a greater angle to the shank than the axis of the hole 58, it can be brought into alignment with the latter by removing a slight amount of metal from the shank by grinding at either or both of the regions designated at a and b in FIG. 7; if originally at a lesser angle, by grinding in the regions 0 and/or d.

In the tool as thus described, the tip 50 can be worn down from an initial length of one-half inch to a final length of one-eighth inch (its minimum useful length), without materially altering the wave pattern or the form of the ellipse.

FIG. 11 has shown the lateral wave mode as having two nodes. This is the minimum number, but by certain design modifications, additional nodal points will occur, and such designs do not depart from the scope of the invention.

In FIGS. 12-14 I have shown a modified magnetostriction driver and adapter assembly 64, and a modified shank 70 of the pin-insert type, generally similar to that of FIGS. 7-9, and designed to have longitudinal and lateral standing wave patterns similar to those shown in FIGS. I 10 and 11, respectively. The magnetostriction driver and adapter may be generally as in FIG. 1, comprising wound core 65, to which is fixed an adapter 66 which, however, is somewhat more massive, and shorter than that of FIG. 1. The shank '70 has at its upper end a taper threaded coupling pin or plug 71, above a hexsection shank head 72, the coupling element 71 being screwed into the taper threaded socket 63 of adapter 66. The hex-section shank head affords wrench engaging faces 73. The shank 70 curves longitudinally, much as shank 44 of FIG. 7, and has at its lower end an angular, cylindrical pin holder head 74 formed with a tapered hole 75 for a replaceable tapered drill tip pin 76, just as in FIG. 7.

Starting from lines 79, across or at the bottom of two opposite hex-faces 73, located approximately one-third of the length of the shank from the top of the hex-section portion thereof down to the upper end of pin holder head 74, the shank is gradually tapered, as at 80, to a thin section 81, of thickness just slightly less than the diameter of cylindrical pin holder head 74, and this thin section 81 merges with head 74, as shown. The center of gravity of head 74 will be observed to be displaced off the central longitudinal axis established by the threaded coupling pin 71 and the hex-section 72.

The front side of the shank 70 is defined by a long curved surface 82 starting from the nose 83 of head '74, extending therefrom inwardly to a point of tanqency, ap-

proximately opposite lines 79, with a plane defined by hex- 95, to intersect the hex-shaped shank head 72 along lines I 96. The curved surface 90 is approximately tangent, in its concave region 93, with a plane defined by hex-head edges 97; and is also substantially tangent, in its convex region 92, with a prolongation of edge 98 of hex-head 72. The widest portion of the shank, formed by concave curve 92, occurs approximately midway of the length of the shank.

It will be observed that the shank has been materially thinned, as viewed in the aspect of FIG. 12, in the region of the bottom of the curved region 93, but is tluck at that point in the direction at right angles thereto, i.e., as seen in FIGS. 13 and 14. This thinning affords localized flexibility and enhanced capability for transverse elastic bending in the section opposite the bottom of the curve 93, which contribute materially to the fixing of the upper lateral wave node within the region of the coupling pin 71.

The essential mass of the pin-insert holder head 74 in this type of shank is fairly substantial, but to attain good amplitude of longitudinal vibration, it should still be of materially less mass than the mass in the region of the coupling to the adapter. To increase amplitude, the adapter 66 has been made of increased mass, i.e., enlarged cross section, at the coupling point with the shank, with some degree of sacrifice of the taper feature characteristic of the adapter of FIG. 1, and some degree of sacrifice of the concentration or lumping of mass at the end of the adapter. The concentration of mass at the coupling end is still, however, preferably somewhat less that at the driven end, so that some taper is retained. Withouta substantial lumped mass at the end of the adapter, the upper lateral wave node does not easily or naturally remain fixed when attempts are made to detune the lateral wave, i.e., to raise its resonant frequency above that of the longitudinal wave. Instead, it tends to climb higher into the adapter, lengthening the wavelength, and the resonant frequency is not materially increased. However, by virtue of the described thinning of the shank in the region 93, and resulting increased flexibility at that point, the upper lateral node is held more or less fixed, the wavelength does not change, and it becomes easily possible to raise the resonant frequency of the lateral wave, which, as will be recalled, is necessary to accomplish the required elliptical motion path.

Such increase in the resonant frequency of the lateral wave is accomplished by thinning the shank, e.g., assuming it originally to be overthick, by grinding on its side surfaces to reduce the thickness of section 81. The corresponding removal of mass, notwithstanding a small degree of reduction in stifiness, has the overall effect of raising the resonant frequency. It is also has this effect without materidly affecting the longitudinal wave resonant frequency. Thus the shank is given such shape and dimensions that its lateral wave frequency is higher than that of its longitudinal wave frequency, the two motions therefore go out-of-phase, and the desired elliptical motion path is attained. Again, the preferred ratios of major to minor axis for the ellipse depend upon the extent to which the resonant frequency of the lateral wave is raised above that for the longitudinal wave. Note is finally made of the fact that the described pinching in of the shank, in the aspect of FIG. 12, is accompanied by a corresponding wide section at right angles thereto, as seen in FIGS. 13 and 14, such that while local flexibility has been introduced insofar as the lateral wave is concerned, a corresponding reduction in longitudinal stiffness, such as might unfavorably influence the longitudinal wave, has not been introduced. The longitudinal and lateral Wave patterns are similar to those shown in FIGS. 10 and ll, respectively.

In all of the foregoing examples, it will be understood that an abrasive slurry is used, requiring a transmitter consisting of the end surface of the cutting tip. Moreover, in all examples this transmitter is driven by an elongated structure which functions as a rod member. The invention exists in my discovery that a very advantageous action of the transmitter can be accomplished by effecting the described relationship of the components of motion of the rod member. There are obviously many variations of shape and drive for the rod member which come within the scope of my invention and the appended claims.

I claim:

1. In a sonic dental drill assembly having an oscilla tory driver and drill-shank coupling means secured thereto forming, with a coupled-in drill shank, a longitudinal standing wave system: an angle drill shank coupled to said coupling means and extending generally longitudinally therefrom, an angle tip on said shank, said shank is formed with a longitudinal curve, and terminates in an enlarged tip holder head, said head being formed with a bore extending angularly of said curved shank, and wherein said tip comprises a pin removably fitted in said angular bore said shank having a length to undergo longitudinal, substantially quarter wavelength standing wave action at a longitudinal Wave resonant frequency of the assembly when said oscillatory driver is operated at said resonant frequency, said shank and angle tip being laterally unbalanced, so as to induce a lateral Wave component in said shank derived from said longitudinal wave, and said shank embodying a physical conformation which tunes said lateral wave to a resonant frequency differing from that. of said longitudinal wave to impart to the ex tremity of said tip an elliptical motion path, and to an extent holding the amplitude of the lateral component of motion to a lesser magnitude than that of the longitudinal component of motion, whereby the major axis of the ellipse extends substantially normal to the extremity thereof.

2. The subject matter of claim 1 wherein said bore and pin are tapered.

3. A one-piece angle drill shank for a sonic dental drill, comprising a threaded coupling pin, a shank projecting from said coupling pin, said shank having opposite side faces tapering in width from said threaded coupling in toward its extremity in one transverse dimension, and being relatively thin from a point near said coupling pin to its extremity in the direction at right angles to said faces, said shank comprising a portion extending longitudinally from said coupling pin, and a tip portion bent angularly to said longitudinally extending portion, the bend in said shank being in a plane at right angles to said opposite side faces.

4. The subjectrnatter of claim 3, wherein the cross sectional area of said shank is materially reduced in the region of said bend.

5. A pin-insert angle drill for a sonic dental drill, comprising a shank, a thickened head at the upper end of said shank including a threaded coupling element, said shank having a gradual longitudinal curve between said coupling element and its remote end, and an enlarged pin holder head on said remote end of said shank, with its center of gravity laterally offset from a longitudinal axis established by said threaded coupling element, and there being a hole through said head, at an angle to said longitudinal axis, for receiving a pin-insert drill tip.

6. The subject matter of claim 5, wherein said shank is so dimensioned that when longitudinally driven through said coupling element from an ultrasonic oscillatory driver, a longitudinal quarter wavelength standing wave is generated therein, with a node located in the region of said threaded coupling element, and wherein said shank is of such lateral unbalance and of such lateral thinness as to undergo also a lateral wave having nodes in the region of the threaded coupling element, and at the upper portion of the pin holder head, and which lateral wave is so out-of-phase with said longitudinal wave that points of the holder head along said pin-insert hole describe elliptical paths whose major axis is parallel to said hole.

7. A pin-insert angle drill shank for a sonic dental drill, comprising: a shank of greater width than breadth throughout the major portion of its length, an enlarged head including a threaded coupling element integrally formed on one end of said shank, said shank extending substantially axially from said threaded coupling element for a distance but curving away from the coupling axis toward its remote end in the plane of its greatest width, and an integral pin holder head at said remote end of said shank formed with a pin-insert hole extending angularly of said curved shank.

8. The subject matter of claim 7, wherein said shank has substantially the cross section of an I-beam.

9. The subject matter of claim 7, wherein said shank, when longitudinally driven at resonant frequency from a sonic oscillatory driver, manifests a longitudinal quarter wavelength standing wave, with a node located in the region of the coupling element, and wherein said shank is of such lateral unbalance and of such lateral thinness as to undergo also a lateral wave having nodes in the region of the threaded coupling element, and at the upper portion of the pin holder head, and which lateral wave is so out-of-phase with said longitudinal wave that points of the holder head along said pin-insert hole describe elliptical paths whose major axis is parallel to said hole.

10. A pin-insert angle drill shank for a sonic dental drill, comprising: a shank having at one end a thick bar section terminating in a threaded coupling, said shank having opposed faces converging from said bar section and thence becoming parallel to form a thin beam section, a pin holder head on the end of said beam section, located with its center of gravity displaced laterally from the longitudinal axis established by said bar section and coupling, said pin holder head having a pin-insert holder extending at an angle to said axis in a plane through said axis and parallel to said parallel opposed face portions of said shank, and said shank being laterally indented in planes parallel to said last mentioned plane in the region of the juncture of said opposed converging faces with said bar to give localized flexibility for lateral bending in said planes.

11. A pin-insert angle drill shank for a sonic dental drill, comprising: a shank, a thickened head at one end thereof, including a threaded coupling element, a pin holder head at the other end of said shank located with its center of gravity offset laterally from a longitudinal axis established by said coupling element, said pin holder head comprising an elongated substantially semicylindric body oriented at an angle to said axis, a taper pin hole through said semicylindric head along the longitudinal axis thereof, said pin holder head having a toe portion at one end and heel portion at the other merging with opposite edges of said shank, and a taper pin drill tip seated in said taper hole and protruding both from said toe portion and said heel portion.

12. A pin-insert angle drill shank for a sonic dental drill, comprising: a shank, a thickened head at one end thereof, including a threaded coupling element, a pin holder head at the other end of said shank located with its center of gravity offset laterally from a longitudinal axis established by said coupling element, and said pin holder head having a pin receiving hole therein whose axis is at an acute angle to said longitudinal axis.

13. The subject matter of claim 12, wherein said pin holder head has toe and heel portions, and said hole extends through said head with a convergent taper from said toe to said heel, and a taper pin drill tip seated in said tapered hole and protruding from said toe portion.

14. A pin-insert angle drill for a sonic dental drill, comprising: a shank, a thickened head at one end thereof, including a threaded coupling element, a pin holder head at the other end of said shank located with its center of gravity offset laterally from a longitudinal axis established by said coupling element, said pin holder head having a pin receiving hole therein on an axis which is angularly disposed to said longitudinal axis, said shank being longitudinally elastically vibratory in substantially a quarterwave length longitudinal standing wave pattern when driven through said coupling element at a predetermined resonant frequency, and said shank and pin holder head in combination giving lateral unbalance to said shank so as to cause said shank to vibrate laterally with a component of motion at an acute angle to said longitudinal axis as well as in said longitudinal standing wave pattern, said pin receiving hole in said pin holder head being substantially parallel to the direction of said lateral vibration, and said shank and pin holder head having a distribution of elasticity and mass causing said lateral vibration to be resonant at a frequency differing from that of the longitudinal resonant frequency of the longitudinal vibration of said shank.

References Cited in the file of this patent UNITED STATES PATENTS 1,966,446 Hayes July 17, 1934 2,990,616 Balamuth et a1. July 4, 1961 FOREIGN PATENTS 745,611 France Feb. 21, 1933 

1. IN A SONIC DENTAL DRILL ASSEMBLY HAVING AN OSCILLATORY DRIVER AND DRILL-SHANK COUPLING MEANS SECURED THERETO FORMING, WITH A COUPLED-IN DRILL SHANK, A LONGITUDINAL STANDING WAVE SYSTEM: AN ANGLE DRILL SHANK COUPLED TO SAID COUPLING MEANS AND EXTENDING GENERALLY LONGITUDINALLY THEREFROM, AN ANGLE TIP ON SAID SHANK, SAID SHANK IS FORMED WITH A LONGITUDINAL CURVE, AND TERMINATES IN AN ENLARGED TIP HOLDER HEAD, SAID HEAD BEING FORMED WITH A BORE EXTENDING ANGULARLY OF SAID CURVED SHANK, AND WHEREIN SAID TIP COMPRISES A PIN REMOVABLY FITTED IN SAID ANGULAR BORE SAID SHANK HAVING A LENGTH TO UNDERGO LONGITUDINAL, SUBSTANTIALLY QUARTER WAVELENGTH STANDING WAVE ACTION AT A LONGITUDINAL WAVE RESONANT FREQUENCY OF THE ASSEMBLY WHEN SAID OSCILLATORY DRIVER IS OPERATED AT SAID RESONANT FREQUENCY, SAID SHANK AND ANGLE TIP BEING LATERALLY UNBALANCED, SO AS TO INDUCE A LATERAL WAVE COMPONENT IN SAID SHANK DERIVED FROM SAID LONGITUDINAL WAVE, AND SAID SHANK EMBODYING A PHYSICAL CONFORMATION WHICH TUNES SAID LATERAL WAVE TO A RESONANT FREQUENCY DIFFERING FROM THAT OF SAID LONGITUDINAL WAVE TO IMPART TO THE EXTREMITY OF SAID TIP AN ELLIPTICAL MOTION PATH, AND TO AN EXTENT HOLDING THE AMPLITUDE OF THE LATERAL COMPONENT OF MOTION TO A LESSER MAGNITUDE THAN THAT OF THE LONGITUDINAL COMPONENT OF MOTION, WHEREBY THE MAJOR AXIS OF THE ELLIPSE EXTENDS SUBSTANTIALLY NORMAL TO THE EXTREMITY THEREOF. 